| Co-Investigator(Kenkyū-buntansha) |
RAKUGI Masami Osaka Univ., Faculty of Dentistry, Assistant Professor, 歯学部, 講師 (60191681)
OOSHIMA Takashi Osaka Univ., Faculty of Dentistry, Associate Professor, 歯学部, 助教授 (80116003)
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| Budget Amount *help |
¥6,500,000 (Direct Cost: ¥6,500,000)
Fiscal Year 1991: ¥900,000 (Direct Cost: ¥900,000)
Fiscal Year 1990: ¥5,600,000 (Direct Cost: ¥5,600,000)
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| Research Abstract |
To developed a pit and fissure sealant, we produced several trial cements combining tetracalcium phosphate (4CP) and CaF_2 or SrF_2. We investigated their properties as well as their adhesion to enamel, and found the most promising compositions of the liquid and of the cement powder recording their optimum powder-liquid ratio. We also investigated the changes in each cement mixture when immersed in phosphate buffered saline. The liquid consisted of 50wt% water, 30wt% polyacrylic acid (mixture of various ratios of 2 kinds which differed in number- average molecular weigtht), 15wt% citric acid, and 5wt% tartaric acid. By changing the ratio of the 2 kinds of polyacrylic acid, we obtained 5 kinds of liquid. They were mixed with 4CP and their setting times, compressive strengths (according to the ADA specification NO. 61 for polycarboxylate cements), and adhesion to enamel were measured. Using 25wt% polyacrylic acid whose number-average molecular weight was 5000 and 5wt% polyacrylic acid wh
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ose number-average molecular weight was 12000, we obtained a mixture had the widest utility, high adhesion, and high compressive strength. We then made 4 kinds of powers consisting of 4CP and/or CaF_2((1)4CP, (2)99wt%4CP-1wt%CaF_2, (3)90wt%4CP-10wt%CaF_2, and (4)70wt%4CP-30wt%CaF_2) and 2 kinds of powders consisting of 4CP and SrF_2((1)98wt%4CP-2wt%SrF_2, (2)90wt%4CP-10wt%SrF_2). We mixed them with the liquid stated above and each mixture was examined on the same properties. It was found that no more than 30wt% CaF_2 or 2wt% SrF_2 didn't decrease their compressive strength. We also immersed these mixtures in phosphate buffered saline, and examined how their 4CP converted to HAP by CHI-ray diffraction and infrared spectroscopy. The result indicated the presence of CaF_2 stimulated 4CP to convert to hydroxyapatite. To evaluate the effect of these 4CP cements on enamel, we examined the release of F, Ca, and P from them and their recalcificalcifying effect on subsurface caries lesion. The powder (99wt%4CP-1wt%CaF_2) was found to be best for clinical use. In 20 patients, fissures of erupting first molars were filled with this cement, while fissures of the other erupting first molars were observed as controls. After 18 months, caries occurrence of filled first molars was 33% less than that of controls. These results suggest that this trial cement has great potential as a pit and fissure sealant. Less
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